Pharmacokinetics & Pharmaceutics

Absorption, Distribution, Metabolism, and Excretion (Elimination) — the four processes that describe what the body does to a drug.

Pharmacokinetics (PK) = what the body does to the drug (ADME). Pharmacodynamics (PD) = what the drug does to the body (concentration-effect relationship, receptor interaction).

Bioavailability (F) is the fraction of an administered dose that reaches the systemic circulation unchanged. IV dosing has F = 1 (100%) by definition; other routes are usually <1.

F = (AUC_oral × Dose_IV) / (AUC_IV × Dose_oral). It compares the systemic exposure of an extravascular route to that of IV.

Metabolism of an orally absorbed drug by the gut wall and liver before it reaches systemic circulation, reducing bioavailability. Relevant for high-extraction drugs (e.g., propranolol, lidocaine, nitroglycerin, morphine).

IV, IM, SubQ, sublingual/buccal, transdermal, inhalation, and rectal (partially) bypass or reduce first-pass hepatic metabolism; oral and (mostly) rectal upper portion do not.